1,272 research outputs found
Redox functionality mediated by adsorbed oxygen on a Pd-oxide film over a Pd(100) thin structure: A first-principles study
Stable oxygen sites on a PdO film over a Pd(100) thin structures with a
(sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the
first-principles electronic structure calculations with the generalized
gradient approximation. The adsorbed monatomic oxygen goes to a site bridging
two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd
atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO
oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by
oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen atom
between the two stable sites is evaluated using the nudged elastic band method,
where an energy barrier for a translational motion of the adsorbed oxygen may
become sim 0.45 eV, which is low enough to allow fluxionality of the surface
oxygen at high temperatures. The oxygen fluxionality is allowed by existence of
2-fold-coordinated Pd atoms on the PdO film, whose local structure has
similarity to that of Pd catalysts for the Suzuki-Miyaura cross coupling.
Although NO_x (including NO_2 and NO) reduction is not always catalyzed only by
the PdO film, we conclude that there may happen continual redox reactions
mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the
influx of NO_x and CO continues, and when the reaction cycle is kept on a
well-designed oxygen surface.Comment: 15 pages, 6 figures, submitted to J. Phys. Condens. Matte
Spectral function of the spiral spin state in the trestle and ladder Hubbard model
Eder and Ohta have found a violation of the Luttinger rule in the spectral
function for the t-t'-J model, which was interpreted as a possible breakdown of
the Tomonaga-Luttinger(TL) description in models where electrons can pass each
other. Here we have computed the spin correlation along with the spectral
function for the one-dimensional t-t' Hubbard model and two-leg Hubbard ladder.
By varying the Hubbard U we have identified that such a phenomenon is in fact a
spinless-fermion-like behavior of holes moving in a spiral spin configuration
that has a spin correlation length of the system size.Comment: 3 pages, RevTex, 8 figures in Postscript, to be published in Phys.
Rev. B (rapid communication
Solution to Big-Bang Nucleosynthesis in Hybrid Axion Dark Matter Model
Following a recent suggestion of axion cooling of photons between the
nucleosynthesis and recombination epochs in the Early Universe, we investigate
a hybrid model with both axions and relic supersymmetric particles. In this
model we demonstrate that the 7Li abundance can be consistent with observations
without destroying the important concordance of deuterium abundance.Comment: 5 pages, 3 figure
Spin-twist driven persistent current in a strongly correlated two-dimensional electron system: a manifestation of the gauge field
A persistent current, coupled with the spin state, of purely many-body origin
is shown to exist in Nagaoka's ferromagnetic state in two dimensions (2D). This
we regard as a manifestation of a gauge field, which comes from the surrounding
spin configuration and acts on the hole motion, being coupled to the
Aharonov-Bohm flux. This provides an example where the electron-electron
interaction exerts a profound effect involving the spins in clean
two-dimensional lattice systems in sharp contrast to continuum or spinless
fermion systems.Comment: 11 pages, typeset using Revtex 3.0, Phys. Rev. B in press, 2 figures
available upon request at [email protected]
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